Hot melt adhesives are widely used in industry for various applications such as product assembly and packaging, including particularly, for use in cardboard case sealing and carton closing operations. Some of these operations (e.g. for cartons, cases or trays used for packaging molten cheese at 60.degree. C. and its subsequent storage at freezer temperatures of -18.degree. to -6.degree. C. or for packaging yogurt or freshly baked goods at temperatures greater than about 40.degree. C.) require a hot melt adhesive with exceptionally high heat resistance (ability to maintain a fiber tearing bond at elevated temperatures) without sacrificing good cold resistance (ability to maintain a high strength bond in the cold with no tendency to fracture). Moreover, the viscosity of such adhesives must be low enough and the set speed fast enough to give good machinability, for example, on rapid-fire, automatic equipment with short compression sections which are used in commercial case or carton operations. The thermal stability and aesthetics also must be such as to produce no charring, skin, or gel formation coupled with a small viscosity change followed prolonged aging at typical operating temperatures (e.g. 175.degree. C.) so as to minimize down time for maintenance and to provide consistent application patterns and amounts during operation. These aesthetic considerations have become more important in recent years as customers increasingly demand hot melt adhesives having pot clarity, i.e. adhesives which are clear in their molten form.
Hot melt case and carton sealing products available and in commercial use today (primarily polyethylene and ethylene vinyl acetate formulations) lack one or more of the previously described propoperties; (1) high temperature end use performance; (2) low temperature end use performance; (3) clean machining; (4) low viscosity; (5) desireable aesthetics (clarity); (6) satisfactory thermal stability; (7) and/or low cloud point (below 120.degree. C.). It would therefore be an advance in the art to provide another hot melt adhesive having good bond strengths (i.e., producing fiber tear) at both high and low temperatures coupled with low viscosity, fast set speed and excellent thermal stability, machining and aesthetics.